Computer only beeps on Startup

I'm hoping someone can help me out with something I haven't tried. I recently replaced the heatsink on my AMD Athlon XP 2600+ processor and now when I turn the computer on, it only beeps. The beeping is continuous and lasts about 1-2 seconds. I researched on here and changed out the memory and video card, but nothing works. Anyone got anymore ideas? Anything would be great!

Yes, I had removed all the thermal grease from before, but I will try reseating it again. I wasn't sure if that might be what was causing it. Just to make sure, I got a Antec CPU Cooler for a Socket A, this should work right?